1. Field of the Invention
The present invention relates to a system for automatically removing unwanted films from the surfaces of spacecraft. More specifically, this invention is concerned with methods and means for removing layers of organic matter which are tightly bound by the polymerizing action of the sun's ultraviolet radiation to critically important surfaces of vehicles in space.
2. Background Information
Once a spacecraft is exposed to the hostile environment beyond the upper strata of the earth's atmosphere, microscopic substances present in space as well as particles liberated from the spacecraft itself form occluding layers over sensitive surfaces which serve as interfaces for the passage of radiation in and out of the craft. These unwanted substances are attracted to surfaces by electrostatic forces or are deposited on the exterior of a vehicle after a random collision as the craft moves along its course in space. After these particulates adhering to the spacecraft are irradiated by the sun's ultraviolet rays, they bond together and to the radiation interface surfaces on the exterior of the satellite. The sun's energy helps form long chains of organic molecules called polymers which are difficult to remove from these important sensor and communication regions of the vehicle.
Once a sensor or radiation aperture is covered with a partially opaque coating, the efficiency and efficacy of the entire space system is placed in great jeopardy. The transmission of vital radio, infrared, optical, or laser signals may be impaired or precluded. The capacity of an orbiting sensor platform which collects, stores, or analyzes radiation from the earth's surface or atmosphere in order to help scientists conduct research may be severely diminished. A satellite which depends upon celestial navigation techniques to remain on course and at the proper altitude can become completely useless if the objective lens of its star sensor is obscured by a shading scale of space debris.
Nearly every craft launched into space suffers from the inevitable reduction in operational effectiveness that results from the formation of these contaminant coatings. An increasing number of scientific, military, and commercial endeavors have begun to reap the benefits of the exploitation of the regions above our atmosphere. Space-based telescopes have extended the earthbound limits of astronomical observation. Remote sensing from orbit is the basis of modern methods of military surveillance and weather forecasting. Orbital detection systems play a critical role in studies concerning earthquake detection, agricultural yields, changes in the world's oceans, and exploration for petroleum and other scarce mineral resources. The utility of virtually all of these expensive systems is slowly but inescapably attenuated by the gradual build up of these unwelcome veneers.
There currently exists no prior methods or devices known to the inventor which may be employed to automatically clean radiation aperture surfaces by removing these deleterious organic films from a spacecraft in orbit. If the particulates clinging to exterior sensors and radiators have never been exposed to ultraviolet radiation, they are not converted into stubborn, strongly adhesive polymers and may be dispersed by simple sublimation if the coated substrate surface can be sufficiently heated. Since all external areas of a space vehicle in orbit are eventually illuminated by the sun, the sublimation of contaminants by heating is a solution which offers few practical advantages.
For space vehicles in low orbits, some cleaning can occur if critical surfaces are positioned so that they face the direction of motion of the craft. In this way, traces of atmospheric oxygen which are present sixty to one hundred miles up may impinge upon the organic films and eradicate them via oxidation reactions. This technique is only marginally effective and is limited to vehicles like the space shuttle which are constrained to operate within a very narrow range of low altitudes. The vast majority of craft which require sensor and power surface cleaning circumnavigate the world in far higher orbits, including geosynchronous satellites which circle the globe over twenty three thousand miles above the earth's surface.
In terrestrial environments, similar organic materials may be dispersed using special lamps under laboratory conditions. Atmospheric oxygen can be converted to its allotropic counterpart, ozone, and atomic oxygen by stimulation with an ultraviolet lamp. The combined effect of the interaction of these gases with the polymerized layers and the ultraviolet energy is the elimination of a few of the uppermost strata of contaminants. The great bulk of the organic coating is not susceptible to this method of ultraviolet-ozone treatment, since many layers are simply re-polymerized by the additional radiation.
High energy beams can be used to bombard surfaces and disband occluding films through kinetic interactions, but they concomitantly damage and destroy the sensitive surfaces which they are intended to restore. These techniques solve the problem by brute force, and are not selective enough to use on spaceborne surfaces which are often enclosed by delicate, protective optical coatings.
None of the methods or devices described above provides an effective solution to the problem of the degradation of spacecraft by organic film obscuration of their vital radiation apertures. An effective solution to this problem would satisfy a long felt need experienced by the aerospace community for over twenty-five years. A truly practical and reliable means for removing undesirable films would represent a major advancement in space technology that would enhance the utility of nearly all future space systems and magnify the opportunities for scientific, military, and commercial enterprise in space. Such a device would ideally be suited to operate in cooperation with a wide variety of space systems and to perform cleaning tasks reliably for a myriad of critical satellite components without harming the underlying hardware.